docs: add AWS deployment & infrastructure guide in README.md

[bhagyashreewagh]

This PR adds a full AWS deployment & infrastructure guide for the Antenna backend.

What’s Included

• New aws-infra/README.md documenting:
  • Elastic Beanstalk (ECS-based) multi-container setup
  • ECR repositories (antenna-backend, antenna-awscli)
  • RDS PostgreSQL configuration
  • ElastiCache Redis (TLS) configuration
  • IAM roles and policies used by EB
  • VPC, subnets, and security group architecture
  • Full deployment workflow (ECR -> EB)
  • Common debugging notes (Redis TLS, EB health checks)
  • Future improvements (Secrets Manager, CI/CD, least privilege IAM)

Why This Matters

The project previously lacked end-to-end infrastructure documentation.
This guide makes it possible for other contributors and lab members to:

• Reproduce the deployment
• Understand AWS resource relationships
• Maintain and safely update the backend stack

Notes

• No application logic changed - documentation only.
• This PR is marked as Draft so the team can review structure and clarity before merging.

[netlify]

✅ Deploy Preview for antenna-preview canceled.

Name	Link
🔨 Latest commit	e449df2
🔍 Latest deploy log	https://app.netlify.com/projects/antenna-preview/deploys/6916f17d7bb54c000894153c

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✨ Finishing touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

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